White light



v April 11, 1933. Q L, 1 BECK 1,903,495

-WHITE LIGHT Original Filed Dec x. 17,- 1929 Qvweutoz 450 L. BECKPatented Apr-.11,

(UNITED STATES PATENT OFFICE LEO L. 0] WESTFIELD, NEW JERSEY, ASSIGNOR,'BY MESNE ASSIGNMENTS, TO

GENERAL TUBE LIGHTS COBIE'OIBIAIIIIOIT, OF NEW YORK, '14. Y, ACOBPOBATION'OF DELAWARE WHITE morn- Lpplioation Med December 17, 1929,Serial No. 414,629. Renewed November 38, 1982.

The present invention is a continuation in part of my co endingapplication, Serial No. 373,916, filed une26, 1929.

1 The invention relates to luminous .tubes which emit a light which doesnot distort the natural colors. It is well knownthat a neon luminoustube which emits the characteristic orange and red colors is rich in redrays and is lacking in blue rays, with the result that the naturalcolors are distorted and do not appear to the eye in their true colors.The disadvantage of neon luminous tubes for illuminating purposes istherefore obvious.

It is an object of this invention to supply red rays to the lightemitted by helium tubes so that the colors of the spectrum are notdistorted.

Another object is to include a rare gas With thehelium which will emit alight having a characteristic color ray which is lacking or notparticularly intense inthe helium color.

It has been found that, in order to secure a light from a luminous tubewhich does not distort the natural colors of objects viewed thereby, byincluding the rare gas neon with v the gas helium in a tube, andrendering the gaseous contents of the tube luminous by the passage of anelectric current, the-gaseous contents will emit a light which does notdistort or materially distort the natural colors. It is to beunderstood, however, that when reference is made to helium or neon gasin the application, a gas is meant which emits the characteristic heliumand neon colors when luminous regardless of whether it contains othergases mixed therewith, so long as the characteristic colorsof thesegases are not masked.

The helium and neon within the tube become luminous upon operation ofthe tube and each gas emits its characteristic color and the proportionsof the gases are so selected that the characteristic color emitted byone gas blends with the characteristic color emitted by the other andthe spectrum of each gas is visible in the light, or to express theresult secured 'in a; difierent manner, the lightemitted spectrum ofeach gas.

by the tube has a permanent -may be operated on low voltage alternatingcurrent.

By including krypton, xenon or argon with the helium and neon, a gaseousmixture is ob tained which has a lower voltage gradient than a mixtureof neon'and helium alone, and results in a more efiicient tube. Thepercentage of one of these gases added may be approximately one half ofone per cent which is not suflicient to eflt'ect the nature of the lightemitted by the tube but materially efiects the voltage gradient orefiiciency of the tube. The term low potential gas will be hereindefined'to mean one of the gases, argon, krypton or xenon, asdistinguished from the other rare gases, and the term low potential gasas used in the claims is to be taken as having this meaning.

The present invention provides a new and improved white light. This termhas a special meaning which has been hereinabove described and relatesto a light which has a rich and well proportioned spectrum approachingthat of sunlight.

The invention provldes a new and improved gaseous dischargedeviceadapted to emit white light and further adapted to o erate at lowvoltages such as are commercia ly obtainable from ordinary electricalsupply circuits.

The invention -provides a new and improved combination of process andapparatus features including acombination of a mixture of gasesadaptedto yield a white light, particularly one in which the com onentsare carefully adjusted and in WhlCh the proportion of the saidcomponents is suitably maintained with an alkali cathode as, forexample, a cathode comprising a pool 1 containing an alkali metal ormixture of alkali metals as, for example, potassium, caesium, lithium,sodium, rubidium.

With a given voltage available, the efliciency of the device may beexpressed in terms of the length of the tube of a given diameter whichcan be satisfactorily operated, since the amount of light is, in such acase, proportional to the length of positive column,'and the length ofthe latter and of the tube as a whole de end upon the potential 5 drothrough the tu e.

e present invention comprises a combination of. a mixture ofgases adated to yield a new and improved white lig t with the following featuresin combination and sub-combination, vizz.

1. I Controlled and adjusted current densities.

2.-Controlled and adjusted as composition in which the proportion o neonis correlated with the current density to yield white light-of thedesired quality.

3. The use of a low potential gas, or gases, in carefull adjustedproportions.

47. A cat ode comprising a pool of alkali metal.

5. An adjustment and control of the total pressure of the gas filling,including that of the vapor of the alkali metal and that'of the heliumand neon, and the correlation of this adjusted and controlled totalpressure, in-

cluding the partial pressure of the neon and helium, with the alkalicathode and with the diameter of the tube.

It has been found that by operating at relatively high currentdensities, the potential fall through the positive column is re-. Iduced thereby and according to the resentinvention, the current densityis a justed .to a suitable range of value as from-0.15 to V 0.60 amperesper square centimeter of crosssection of the positive column. It ishighly desirable to correlate the percentage of neon in the gas mixturewith the particular current density employed inasmuch as with 1ncreasedcurrent densities there is a tendency toward a disturbance ofthebalance'between the proportion of the current carried b the helium andthe neon at lower current ensities, with a consequent disturbance in thecharacter of the spectrum of the mixed ases of such a nature that theintensity 0 the neon light decreases and that of the helium increases.To offset this change and to mainlightemitted by the mixed gases, theproportion of neon is increased as the current density is increased sothat corresponding to the range of current densities specifie above, therange of percentage of neon may vary as, for example, from 2 to 9. percent. A typical gas mixture adapted to ield white light having a wellroportione spectrum at a current density 1n the neighborhood of 0.4amperes per square centimeter of crosssection of the positive column maybe represented by helium 92.25 percent, neon 7 .25 per cent and argon0.50 per cent. As the current density decreases below the value specified, the per cent of neon should decrease,

' and conversely as the current density intain the desiredspectrumcomposition of the creases above the value specified the cent of neonshould increase. Thiscareful adjustment of the relationship between thecurrent density and the per cent of neon in the neon-helium mixture ishighl desirable in order to maintain the well ba anced character of thespectrum of the light emitted by the mixed gases so that the proportionof the various colors in the said spectrum will closely approach theproportion of the same colors in sunlight or other true white light.

Regarding the use of a low potential gas as hereinabove mentioned, ithas already been' Care must be taken,-howcver, that-the per" cent ofthis low potential gas does not exceed certain values in order to avoidreducing the intensity of the light. These gases,

namely, argon, krypton and xenon, have a.

low potential gradient as compared with helium and neon, and tend tocarry the current to the exclusion of the latter, and since theintensity of the light emitted by argon, krypton and xenon is relativelylow, the

result of using such low potential gases in too large a proportion is toreduce the inten sity of the light emitted by the tube. For example, ifthe ercentage of argon in the typical mixture ereinabove described goesmuch above that s ecified therein, namely,

0.50 per cent, the mte ity of the light is considerably reduced. I thecase of krypton,

a similar eifect is observed when the amount thereof exceedsapproximately 0.30 percent, and in the case of xenon it is undesirableto use more than about 0.15 per cent. Krypton and xenon are, therefore,distinguished in their properties in this connection from argon and fromeach other, since the proportion of krypton or xenon should bemaintained at a lower value than is the case where argon is employed.

Regarding the control and adjustment of the total pressure of thegaseous contents of the tube andthe partial pressure of the rare gasestherein, it has been found that the potential gradient and therefore theefliciency of the tube, when employed in connection with a constant orpredetermined potential such as 220 volts, varies with the pressure ofthe rare gas or gases in a tube of a given diameter and the presentinvention provides in combination with the other features, themaintenance of those ranges of pressure of the rare gases whichcontribute a maximum efiiciency in terms of tube length. Under theinfluence of the heat developed during operation of the tube, avaporization of alkali metal occurs. The total p essure in the tube thenbecomes the sum of the pressure of the rare gases and that of the alkalimetal' ample, in a tube having an outside diameterof millimeters andan'inside diameter of 27 millimeters, the pressure of the rare gases mayvary from 0.3 to 1.5 millimeters as measured in the usual way in termsof mercury, and in a typical case it may be 0.75 millimeters. If, .onthe other hand, the outside diameter of the tube were 11 millimeters andthe inside diameter 8, millimeters, the range of partial pressure of therare gas filling should be about 5 to 7 millimeters. Unless adjustmentof the ressure of the rare gas to make allowance or the generation ofalkali vapor is made, the tube or lamp may be extinguished duringoperation due to the building upof the total pressure by alkali vapor,particularly where the lamp is to be operated at maximum efiiciency,that is to' say, where the length of the tube and the positive column ofthe given diameter is i the maximum that can be operated from the,

source of predetermined otential.

The inventio' will be escribed in greater detail with reference tothe-accompanying drawing which illustrates one embodiment of theapparatus of the invention and of means for the practice of the processthereof. It is intended and will'be understood, that the invention isillustrated by, and not limited to such illustration.

determined potentia such as 220 volts, through the resistance 8 whichmay be variable to the gaseous discharge device includmg the anode 2,the positive column 1, the alkali pool 3 constituting the cathode, andthe metallic contact 4, which may be copper, nickel, iron, and thelike.- Lead-in wires 5 and 12 are connected respectivel with the member4 and the anode 2 throug the usual glass seals or press members 14 and16. The

evice is shown .as adapted to be operated with direct current. In theevent that alternating current is employed double anodes can be usedoperating in conjunction with the cathode. The tube 1 may have anoutside diameter of 30 millimeters and inside diameter of 27millimeters, and theshortest distance between the anode 2 and thesurface of the alkali pool 3 may be 16 inches. By

- adjusting the resistanceS, a current density of 0.15 to 0.60 amperesper square centimeter.

of cross-section of pos1tive column may be supplied. For example, thecurrent density may be 0.40 amperes per square centimeter correspondingto a current of 2.25 amperes. At this current density, the gascomposition may consist of helium 92.25 per cent, neon 7.25 per cent andargon 0.50 per cent,'and will yield a white light havin a wellproportioned spectrum approaching t at of sunlight. The partial pressureof the rare gases should be within a range of 0.3 to 1.5 millimeters, asfor example, 0.7 5 millimeters in order to compensate for the .buildingup of the total pressure of the gaseous contents of the tubeby theformation of alkali vapor. By suitable correlation of the featuresherein described including current density, proportion of helium andneon, the

use of lowpotential gas, theadjustment of the pressure of the raregases, and the use of a cathode comprising an alkali metal as shown, alight having' a well proportioned spectrum approaching that .of sunlightmay,

be obtained at a high efliciency, the latter being expressed in terms oftube length of a" given diameter suchas 25 to 30 millimeters capable ofoperation from a source of current of predetermined potential, and asherein shown the lengthof the positive column between the electrodes 'mabe. approximately gidinches for a tube of t e dimensions speci- Thecathode 3 may comprise any of the metals of the alkali group such aspotassium, caesium, or the like, or mlxtures thereof contained in thebulb liportion 6. .There is a tendency for the a ali metal to creep upalong the inside surface of the member 6 of the tube land to causeblackeningthereof. To' prevent this undesirable phenomenon a trap member10 is provided.

The advantages of the invention have been set forth in some detaila 'dthe preferred em- The generator 7 supplies current at a pre bodimentshave been d cribed. It is to be understood, however, that variouschanges may be made without departing from' the invention or sacrificingany of theadvantages enumerated, or any other advantageous results whichmay be obtained'by an ap lic'ation of the principles and the facts setibrth.

What is claimed is:

1. A gaseous discharge luminous tube device comprisinglin combination anenvelope, an anode, a cat ode comprising a pool of alkali metal, a gasmixture comprising helium and neon, the said device being adapted tooperate at a current density of 0.15 to 0.60 amperes per squarecentimeter of tube crosssection and the gas mixture containing neon inproportion of 3 to 9per cent.

, 2. A gaseous dischar e luminous tube de-' vice comprising in comination'an envelope,- an anode comprising a pool of alkali metal, and agas filling comprising helium and neon, the proportion of neon'beingfrom about 2 t0 9 per cent, the pressure of said gas filling being from0.3 to 1.5 millimeters.

3. The method ofoperating a gaseous discharge luminous tube 'devicewhich com- 4- I M I I I 1,908,495

ture of helium and neon, the pressure of which is from 0.3 to 1.5millimeters, the proportion of neon being from 3 per cent to t 9percent, between an anode and a cathode comprising a pool of alkalimetal and maintaining the current density of the discharge between 0.15and0.60 amperes per square centimeter of tube cross-section. 4. Themethod of operating a gaseous dis- 10 charge luminous tube device whichcomprises passing -a discharge through a mixture of helium, neon and alow potential gas,

the pressure of such gases'being from 0.3 to 1.5 millimeters, theproportion of the neon being from 3 per cent to '9 per cent, between ananode and a cathode comprising a pool-of v alkali metal and maintainingthe current density of the discharge between 0.15 and 0.60 amperes persquare centimeter of tube cross-section.

5. A high eiliciencyv positive column gas, discharge light comprising incombination an envelope, an anode, a cathode comprising a reservoir ofalkali metal, means to supply discharge current density of the order of0.15 to 0.60 amperes per square centimeterof positive column crosssection'and a gas comprising helium and neon blended p toget er toproducea composite light in which the proportion of neon is within therange of 2.0 to 9.0 per cent in which the characteristic helium and neonspectral lines of maximum intensity are both clearly eifective in thecomposite light at current densities 35. of the order described, thepartial pressure v of the helium and neon at ordinary room temperaturebeing within therange which, a augmented by the pressure of alkali metalvapor during operation, corresponds toan 40 optimum low potentialgradient of the positive column, this range being from about 0.3 to 1:5millimeters for tubeshaving an internal diameter of the order of 27millimeters to about 5 to 7 millimeters for tubes p having an internaldiameter of the. order of 8 millimeters, the gas filling also containinga low potential gas the proportion .of which is fwithin the range thatmaterially lowers the potential gradient of the gas mixture as a wholewithout detracting from the color and intensity of the helium neonblended-light, the range being not greater than about 0.5 percent.

- testimony whereof I aflix my signature. LEOLBECK.

